The SDK split the HTTP server scaffolding into the new
checker-sdk-go/checker/server subpackage. Update main.go to import
server and call server.New, and isolate the interactive form code
behind the standalone build tag so plugin/builtin builds skip
net/http entirely.
Follow the checker-sdk-go interface consolidation: reporter methods
now take sdk.ReportContext and read the payload via ctx.Data() instead
of the raw json.RawMessage parameter. Backed by the same underlying
logic.
